3d semiconductor device and structure

ABSTRACT

A 3D semiconductor device, the device including: a first level including a first single crystal layer; first transistors overlaying the first single crystal layer; second transistors overlaying the first transistors; and a second level including a second single crystal layer, the second level overlays the second transistors, where the first transistors and the second transistors each includes a polysilicon channel.

CROSS-REFERENCE OF RELATED APPLICATION

This application is a continuation in part of U.S. patent applicationSer. No. 15/803,732, which was filed on Nov. 3, 2017, which is acontinuation in part of U.S. patent application Ser. No. 14/555,494,which was filed on Nov. 26, 2014, and now is U.S. Pat. No. 9,818,800issued on Nov. 14, 2017, which is a continuation of U.S. patentapplication Ser. No. 13/246,157, which was filed on Sep. 27, 2011 andnow is U.S. Pat. No. 8,956,959 issued on Feb. 17, 2015, which is acontinuation of U.S. patent application Ser. No. 13/173,999, which wasfiled on Jun. 30, 2011 and now is U.S. Pat, No. 8,203,148 issued on Jun.19, 2012, which is a continuation of U.S. patent application Ser. No.12/901,890, which was filed on Oct. 11, 2010, and now is U.S. Pat. No.8,026,521 issued on Sep. 27, 2011, the entire contents of the foregoingare incorporated by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention describes applications of monolithic 3D integration tosemiconductor chips performing logic and memory functions.

2. Discussion of Background Art

Over the past 40 years, one has seen a dramatic increase infunctionality and performance of Integrated Circuits (ICs). This haslargely been due to the phenomenon of “scaling” i.e. component sizeswithin ICs have been reduced (“scaled”) with every successive generationof technology. There are two main classes of components in ComplimentaryMetal Oxide Semiconductor (CMOS) ICs, namely transistors and wires. With“scaling”, transistor performance and density typically improve and thishas contributed to the previously-mentioned increases in IC performanceand functionality. However, wires (interconnects) that connect togethertransistors degrade in performance with “scaling”. The situation todayis that wires dominate performance, functionality and power consumptionof ICs.

3D stacking of semiconductor chips is one avenue to tackle issues withwires. By arranging transistors in 3 dimensions instead of 2 dimensions(as was the case in the 1990s), one can place transistors in ICs closerto each other. This reduces wire lengths and keeps wiring delay low.However, there are many barriers to practical implementation of 3Dstacked chips. These include:

-   -   Constructing transistors in ICs typically require high        temperatures (higher than ˜700° C.) while wiring levels are        constructed at low temperatures (lower than ˜400° C.). Copper or        Aluminum wiring levels, in fact, can get damaged when exposed to        temperatures higher than ˜400° C. If one would like to arrange        transistors in 3 dimensions along with wires, it has the        challenge described below. For example, let us consider a 2        layer stack of transistors and wires i.e. Bottom Transistor        Layer, above it Bottom Wiring Layer, above it Top Transistor        Layer and above it Top Wiring Layer. When the Top Transistor        Layer is constructed using Temperatures higher than 700° C., it        can damage the Bottom Wiring Layer.    -   Due to the above mentioned problem with forming transistor        layers above wiring layers at temperatures lower than 400° C.,        the semiconductor industry has largely explored alternative        architectures for 3D stacking. In these alternative        architectures, Bottom Transistor Layers, Bottom Wiring Layers        and Contacts to the Top Layer are constructed on one silicon        wafer. Top Transistor Layers, Top Wiring Layers and Contacts to        the Bottom Layer are constructed on another silicon wafer. These        two wafers are bonded to each other and contacts are aligned,        bonded and connected to each other as well. Unfortunately, the        size of Contacts to the other Layer is large and the number of        these Contacts is small. In fact, prototypes of 3D stacked chips        today utilize as few as 10,000 connections between two layers,        compared to billions of connections within a layer. This low        connectivity between layers is because of two reasons: (i)        Landing pad size needs to be relatively large due to alignment        issues during wafer bonding. These could be due to many reasons,        including bowing of wafers to be bonded to each other, thermal        expansion differences between the two wafers, and lithographic        or placement misalignment. This misalignment between two wafers        limits the minimum contact landing pad area for electrical        connection between two layers; (ii) The contact size needs to be        relatively large. Forming contacts to another stacked wafer        typically involves having a Through-Silicon Via (TSV) on a chip.        Etching deep holes in silicon with small lateral dimensions and        filling them with metal to form TSVs is not easy. This places a        restriction on lateral dimensions of TSVs, which in turn impacts        TSV density and contact density to another stacked layer.        Therefore, connectivity between two wafers is limited.

It is highly desirable to circumvent these issues and build 3D stackedsemiconductor chips with a high-density of connections between layers.To achieve this goal, it is sufficient that one of three requirementsmust be met: (1) A technology to construct high-performance transistorswith processing temperatures below ˜400° C.; (2) A technology wherestandard transistors are fabricated in a pattern, which allows for highdensity connectivity despite the misalignment between the two bondedwafers; and (3) A chip architecture where process temperature increasebeyond 400° C. for the transistors in the top layer does not degrade thecharacteristics or reliability of the bottom transistors and wiringappreciably. This patent application describes approaches to addressoptions (1), (2) and (3) in the detailed description section. In therest of this section, background art that has previously tried toaddress options (1), (2) and (3) will be described.

There are many techniques to construct 3D stacked integrated circuits orchips including:

-   -   Through-silicon via (TSV) technology: Multiple layers of        transistors (with or without wiring levels) can be constructed        separately. Following this, they can be bonded to each other and        connected to each other with through-silicon vias (TSVs).    -   Monolithic 3D technology: With this approach, multiple layers of        transistors and wires can be monolithically constructed. Some        monolithic 3D and 3DIC approaches are described in U.S. Pat.        Nos. 8,273,610, 8,298,875, 8,362,482, 8,378,715, 8,379,458,        8,450,804, 8,557,632, 8,574,929, 8,581,349, 8,642,416,        8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,        8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173,        9,030,858, 9,117,749, 9,142,553, 9,219,005, 9,385,058,        9,406,670, 9,460,978, 9,509,313, 9,640,531, 9,691,760,        9,711,407, 9,721,927, 9,799,761, 9,871,034, 9,953,870,        9,953,994, 10,014,292, 10,014,318; and pending U.S. Patent        Application Publications and applications, Ser. Nos. 14/642,724,        15/150,395, 15/173,686, 62/651,722; 62/681,249, 62/713,345,        62/770,751; and PCT Applications (and Publications):        PCT/US2010/052093, PCT/US2011/042071 (WO2012/015550),        PCT/US2016/52726 (WO2017053329), PCT/US2017/052359        (WO2018/071143), PCT/US2018/016759 (WO2018144957), and        PCT/US2018/52332 (WO 2019/060798). The entire contents of the        foregoing patents, publications, and applications are        incorporated herein by reference.    -   Electro-Optics: There is also work done for integrated        monolithic 3D including layers of different crystals, such as        U.S. Pat. Nos. 8,283,215, 8,163,581, 8,753,913, 8,823,122,        9,197,804, 9,419,031 and 9,941,319. The entire contents of the        foregoing patents, publications, and applications are        incorporated herein by reference.

U.S. Pat. No. 7,052,941 from Sang-Yun Lee (“S-Y Lee”) describes methodsto construct vertical transistors above wiring layers at less than 400°C. In these single crystal Si transistors, current flow in thetransistor's channel region is in the vertical direction. Unfortunately,however, almost all semiconductor devices in the market today (logic,DRAM, flash memory) utilize horizontal (or planar) transistors due totheir many advantages, and it is difficult to convince the industry tomove to vertical transistor technology.

A paper from IBM at the Intl. Electron Devices Meeting in 2005 describesa method to construct transistors for the top stacked layer of a 2 chip3D stack on a separate wafer. This paper is “Enabling SOI -BasedAssembly Technology for Three-Dimensional (3D) Integrated Circuits(ICs),” IEDM Tech. Digest, p. 363 (2005) by A. W. Topol, D. C. LaTulipe, L. Shi, et al. (“Topol”). A process flow is utilized to transferthis top transistor layer atop the bottom wiring and transistor layersat temperatures less than 400° C. Unfortunately, since transistors arefully formed prior to bonding, this scheme suffers from misalignmentissues. While Topol describes techniques to reduce misalignment errorsin the above paper, the techniques of Topol still suffer frommisalignment errors that limit contact dimensions between two chips inthe stack to >130 nm.

The textbook “Integrated Interconnect Technologies for 3D NanoelectronicSystems” by Bakir and Meindl (“Bakir”) describes a 3D stacked DRAMconcept with horizontal (i.e. planar) transistors. Silicon for stackedtransistors is produced using selective epitaxy technology or laserrecrystallization. Unfortunately, however, these technologies havehigher defect density compared to standard single crystal silicon. Thishigher defect density degrades transistor performance.

In the NAND flash memory industry, several organizations have attemptedto construct 3D stacked memory. These attempts predominantly usetransistors constructed with poly-Si or selective epi technology as wellas charge-trap concepts. References that describe these attempts to 3Dstacked memory include “Integrated Interconnect Technologies for 3DNanoelectronic Systems”, Artech House, 2009 by Bakir and Meindl(“Bakir”), “Bit Cost Scalable Technology with Punch and Plug Process forUltra High Density Flash Memory”, Symp. VLSI Technology Tech. Dig. pp.14-15, 2007 by H. Tanaka, M. Kido, K. Yahashi, et al. (“Tanaka”), “AHighly Scalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash UsingJunction-Free Buried Channel BE-SONOS Device,” Symposium on VLSITechnology, 2010 by W. Kim, S. Choi, et al. (“W. Kim”), “A HighlyScalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash UsingJunction-Free Buried Channel BE-SONOS Device,” Symposium on VLSITechnology, 2010 by Hang-Ting Lue, et al. (“Lue”) and “Sub-50 nmDual-Gate Thin-Film Transistors for Monolithic 3-D Flash”, IEEE Trans.Elect. Dev., vol. 56, pp. 2703-2710, November 2009 by A. J. Walker(“Walker”). An architecture and technology that utilizes single crystalSilicon using epi growth is described in “A Stacked SONOS Technology, Upto 4 Levels and 6 nm Crystalline Nanowires, with Gate-All-Around orIndependent Gates (ΦFlash), Suitable for Full 3D Integration”,International Electron Devices Meeting, 2009 by A. Hubert, et al(“Hubert”). However, the approach described by Hubert has somechallenges including use of difficult-to-manufacture nanowiretransistors, higher defect densities due to formation of Si and SiGelayers atop each other, high temperature processing for long times,difficult manufacturing, etc.

It is clear based on the background art mentioned above that inventionof novel technologies for 3D stacked chips will be useful.

SUMMARY

The invention may be directed to multilayer or Three DimensionalIntegrated Circuit (3D IC) devices and fabrication methods.

In one aspect, a 3D semiconductor device, the device comprising: a firstlevel comprising a first single crystal layer; first transistorsoverlaying said first single crystal layer; second transistorsoverlaying said first transistors; and a second level comprising asecond single crystal layer, said second level overlays said secondtransistors, wherein said first transistors and said second transistorseach comprises a polysilicon channel

In another aspect, a 3D semiconductor device, the device comprising: afirst level comprising a first single crystal layer; first transistorsoverlaying said first single crystal layer; second transistorsoverlaying said first transistors; and a second level comprising asecond single crystal layer, said second level overlaying said secondtransistors, wherein said first transistors and said second transistorsare junction-less transistors.

In another aspect, a 3D semiconductor device, the device comprising: afirst level comprising a first single crystal layer; first transistorsoverlaying said first single crystal layer; second transistorsoverlaying said first transistors; third transistors overlaying saidsecond transistors; fourth transistors overlaying said thirdtransistors; a second level comprising a second single crystal layer,said second single crystal layer overlaying said fourth transistor,wherein said second transistors, said third transistors, and said fourthtransistors are self-aligned, being processed following the samelithography step; and a memory peripheral circuit, wherein said memoryperipheral circuit comprises at least one of said first transistors, andwherein said memory peripheral circuit controls at least one of saidsecond transistors, at least one of said third transistors, and at leastone of said fourth transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciatedmore fully from the following detailed description, taken in conjunctionwith the drawings in which:

FIGS. 1A-1D show different types of junction-less transistors (JLT) thatcould be utilized for 3D stacking;

FIGS. 2A-2K show a zero-mask per layer 3D floating body DRAM;

FIGS. 3A-3J show a zero-mask per layer 3D resistive memory with ajunction-less transistor;

FIGS. 4A-4K show an alternative zero-mask per layer 3D resistive memory;

FIGS. 5A-5G show a zero-mask per layer 3D charge-trap memory;

FIGS. 6A-6B show periphery on top of memory layers;

FIGS. 7A-7E show polysilicon select devices for 3D memory and peripheralcircuits at the bottom according to some embodiments of the currentinvention; and

FIGS. 8A-8F show polysilicon select devices for 3D memory and peripheralcircuits at the top according to some embodiments of the currentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention are now described with reference toFIGS. 1-8, it being appreciated that the figures illustrate the subjectmatter not to scale or to measure. Many figures describe process flowsfor building devices. These process flows, which are essentially asequence of steps for building a device, have many structures, numeralsand labels that are common between two or more adjacent steps. In suchcases, some labels, numerals and structures used for a certain step'sfigure may have been described in previous steps' figures.

FIG. 1A-1D shows that JLTs that can be 3D stacked fall into fourcategories based on the number of gates they use: One-side gated JLTs asshown in FIG. 1A, two-side gated JLTs as shown in FIG. 1B, three-sidegated JLTs as shown in FIG. 1C, and gate-all-around JLTs as shown inFIG. 1D. The JLTS shown may include n+Si 102, gate dielectric 104, gateelectrode 106, n+source region 108, n+ drain region 110, and n+regionunder gate 112. As the number of JLT gates increases, the gate gets morecontrol of the channel, thereby reducing leakage of the JLT at 0V.Furthermore, the enhanced gate control can be traded-off for higherdoping (which improves contact resistance to source-drain regions) orbigger JLT cross-sectional areas (which is easier from a processintegration standpoint). However, adding more gates typically increasesprocess complexity.

Some embodiments of this invention may involve floating body DRAM.Background information on floating body DRAM and its operation is givenin “Floating Body RAM Technology and its Scalability to 32 nm Node andBeyond,” Electron Devices Meeting, 2006. IEDM '06. International, vol.,no., pp.1-4, 11-13 Dec. 2006 by T. Shino, N. Kusunoki, T. Higashi, etal., Overview and future challenges of floating body RAM (FBRAM)technology for 32 nm technology node and beyond, Solid-StateElectronics, Volume 53, Issue 7, Papers Selected from the 38th EuropeanSolid-State Device Research Conference—ESSDERC'08, July 2009, Pages676-683, ISSN 0038-1101, DOI: 10.1016/j.sse.2009.03.010 by TakeshiHamamoto, Takashi Ohsawa, et al., “New Generation of Z-RAM,” ElectronDevices Meeting, 2007. IEDM 2007. IEEE International, vol., no., pp.925-928, 10-12 Dec. 2007 by Okhonin, S.; Nagoga, M.; Carman, E, et al.The above publications are incorporated herein by reference.

FIG. 2A-K describe a process flow to construct a horizontally-orientedmonolithic 3D DRAM. This monolithic 3D DRAM utilizes the floating bodyeffect and double-gate transistors. No mask is utilized on a“per-memory-layer” basis for the monolithic 3D DRAM concept shown inFIG. 2A-K, and all other masks are shared between different layers. Theprocess flow may include several steps in the following sequence.

Step (A): Peripheral circuits with tungsten wiring 202 are firstconstructed and above this a layer of silicon dioxide 204 is deposited.FIG. 2A shows a drawing illustration after Step (A).Step (B): FIG. 2B illustrates the structure after Step (B). A wafer ofp− Silicon 208 has an oxide layer 206 grown or deposited above it.Following this, hydrogen is implanted into the p− Silicon wafer at acertain depth indicated by 214. Alternatively, some other atomic speciessuch as Helium could be (co-)implanted. This hydrogen implanted p−Silicon wafer 208 forms the top layer 210. The bottom layer 212 mayinclude the peripheral circuits 202 with oxide layer 204. The top layer210 is flipped and bonded to the bottom layer 212 using oxide-to-oxidebonding.Step (C): FIG. 2C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane3014 using either a anneal or a sideways mechanical force or othermeans. A CMP process is then conducted. A layer of silicon oxide 218 isthen deposited atop the p− Silicon layer 216. At the end of this step, asingle-crystal p− Si layer 216 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 2D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple p− silicon layers 220 areformed with silicon oxide layers in between.Step (E): FIG. 2E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure, including layer regions of p− silicon 221 and associatedisolation/bonding oxides 222.Step (F): FIG. 2F illustrates the structure after Step (F). Gatedielectric 226 and gate electrode 224 are then deposited following whicha CMP is done to planarize the gate electrode 224 regions. Lithographyand etch are utilized to define gate regions.Step (G): FIG. 2G illustrates the structure after Step (G). Using thehard mask defined in Step (F), p− regions not covered by the gate areimplanted to form n+silicon regions 228. Spacers are utilized duringthis multi -step implantation process and layers of silicon present indifferent layers of the stack have different spacer widths to accountfor lateral straggle of buried layer implants. Bottom layers could havelarger spacer widths than top layers. A thermal annealing step, such asa RTA or spike anneal or laser anneal or flash anneal, is then conductedto activate n+ doped regions.Step (H): FIG. 2H illustrates the structure after Step (H). A siliconoxide layer 230 is then deposited and planarized. For clarity, thesilicon oxide layer is shown transparent, along with word-line (WL) 232and source-line (SL) 234 regions.Step (I): FIG. 2I illustrates the structure after Step (I). Bit-line(BL) contacts 236 are formed by etching and deposition. These BLcontacts are shared among all layers of memory.Step (J): FIG. 2J illustrates the structure after Step (J). BLs 238 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in “Bit Cost Scalable Technology with Punchand Plug Process for Ultra High Density Flash Memory,” VLSI Technology,2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka,H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contactscan be constructed to them. Formation of stair-like structures for SLscould be done in steps prior to Step (J) as well.FIG. 2K shows cross-sectional views of the array for clarity.Double-gated transistors may be utilized along with the floating bodyeffect for storing information.A floating-body DRAM has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels (2) some of the memorycell control lines, e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers, and (4)monocrystalline (or single-crystal) silicon layers obtained by layertransfer techniques such as ion-cut.

With the explanations for the formation of monolithic 3D DRAM withion-cut in this section, it is clear to one skilled in the art thatalternative implementations are possible. BL and SL nomenclature hasbeen used for two terminals of the 3D DRAM array, and this nomenclaturecan be interchanged. Each gate of the double gate 3D DRAM can beindependently controlled for better control of the memory cell. Toimplement these changes, the process steps in FIG. 2 may be modified.Moreover, selective epi technology or laser recrystallization technologycould be utilized for implementing structures shown in FIG. 2A-K.Various other types of layer transfer schemes that have been describedin Section 1.3.4 of the parent application (12/901,890, 8,026,521) canbe utilized for construction of various 3D DRAM structures. Furthermore,buried wiring, i.e. where wiring for memory arrays is below the memorylayers but above the periphery, may also be used. In addition, othervariations of the monolithic 3D DRAM concepts are possible.

While many of today's memory technologies rely on charge storage,several companies are developing non-volatile memory technologies basedon resistance of a material changing. Examples of these resistance-basedmemories include phase change memory, Metal Oxide memory, resistive RAM(RRAM), memristors, solid-electrolyte memory, ferroelectric RAM, MRAM,etc. Background information on these resistive-memory types is given in“Overview of candidate device technologies for storage-class memory,”IBM Journal of Research and Development, vol. 52, no. 4.5, pp.449-464,July 2008 by Burr, G. W.; Kurdi, B. N.; Scott, J. C.; Lam, C.H.; Gopalakrishnan, K.; Shenoy, R. S.

FIGS. 3A-J describe a novel memory architecture for resistance-basedmemories, and a procedure for its construction. The memory architectureutilizes junction-less transistors and has a resistance-based memoryelement in series with a transistor selector. No mask is utilized on a“per-memory-layer” basis for the monolithic 3D resistance change memory(or resistive memory) concept shown in FIG. 3A-J, and all other masksare shared between different layers. The process flow may includeseveral steps that occur in the following sequence.

Step (A): Peripheral circuits 302 are first constructed and above this alayer of silicon dioxide 304 is deposited. FIG. 3A shows a drawingillustration after Step (A).Step (B): FIG. 3B illustrates the structure after Step (B). A wafer ofn+ Silicon 308 has an oxide layer 306 grown or deposited above it.Following this, hydrogen is implanted into the n+ Silicon wafer at acertain depth indicated by 314. Alternatively, some other atomic speciessuch as Helium could be (co-)implanted. This hydrogen implantedn+Silicon wafer 308 forms the top layer 310. The bottom layer 312 mayinclude the peripheral circuits 302 with oxide layer 304. The top layer310 is flipped and bonded to the bottom layer 312 using oxide-to-oxidebonding.Step (C): FIG. 3C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane314 using either an anneal or a sideways mechanical force or othermeans. A CMP process is then conducted. A layer of silicon oxide 318 isthen deposited atop the n+ Silicon layer 316. At the end of this step, asingle-crystal n+ Si layer 316 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 3D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple n+ silicon layers 320 areformed with silicon oxide layers in between.Step (E): FIG. 3E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure, including layer regions of n+ silicon 321 and associatedbonding/isolation oxides 322.Step (F): FIG. 3F illustrates the structure after Step (F). Gatedielectric 326 and gate electrode 324 are then deposited following whicha CMP is performed to planarize the gate electrode 324 regions.Lithography and etch are utilized to define gate regions.Step (G): FIG. 3G illustrates the structure after Step (G). A siliconoxide layer 330 is then deposited and planarized. The silicon oxidelayer is shown transparent in the figure for clarity, along withword-line (WL) 332 and source-line (SL) 334 regions.Step (H): FIG. 3H illustrates the structure after Step (H). Vias areetched through multiple layers of silicon and silicon dioxide as shownin the figure. A resistance change memory material 336 is then deposited(preferably with atomic layer deposition (ALD)). Examples of such amaterial include hafnium oxide, well known to change resistance byapplying voltage. An electrode for the resistance change memory elementis then deposited (preferably using ALD) and is shown as electrode/BLcontact 340. A CMP process is then conducted to planarize the surface.It can be observed that multiple resistance change memory elements inseries with junctionless transistors are created after this step.Step (I): FIG. 3I illustrates the structure after Step (I). BLs 338 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in in “Bit Cost Scalable Technology withPunch and Plug Process for Ultra High Density Flash Memory,” VLSITechnology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun.2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., followingwhich contacts can be constructed to them. Formation of stair-likestructures for SLs could be achieved in steps prior to Step (I) as well.FIG. 3J shows cross-sectional views of the array for clarity.A 3D resistance change memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines, e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gates that aresimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut.

FIGS. 4A-4K describe an alternative process flow to construct ahorizontally-oriented monolithic 3D resistive memory array. Thisembodiment has a resistance-based memory element in series with atransistor selector. No mask is utilized on a “per-memory-layer” basisfor the monolithic 3D resistance change memory (or resistive memory)concept shown in FIGS. 4A-4K, and all other masks are shared betweendifferent layers. The process flow may include several steps asdescribed in the following sequence.

Step (A): Peripheral circuits with tungsten wiring 402 are firstconstructed and above this a layer of silicon dioxide 404 is deposited.FIG. 4A shows a drawing illustration after Step (A).Step (B): FIG. 4B illustrates the structure after Step (B). A wafer ofp− Silicon 408 has an oxide layer 406 grown or deposited above it.Following this, hydrogen is implanted into the p− Silicon wafer at acertain depth indicated by 414. Alternatively, some other atomic speciessuch as Helium could be (co-)implanted. This hydrogen implanted p−Silicon wafer 408 forms the top layer 410. The bottom layer 412 mayinclude the peripheral circuits 402 with oxide layer 404. The top layer410 is flipped and bonded to the bottom layer 412 using oxide-to-oxidebonding.Step (C): FIG. 4C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane414 using either a anneal or a sideways mechanical force or other means.A CMP process is then conducted. A layer of silicon oxide 418 is thendeposited atop the p− Silicon layer 416. At the end of this step, asingle-crystal p− Si layer 416 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 4D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple p− silicon layers 420 areformed with silicon oxide layers in between.Step (E): FIG. 4E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure, including layer regions of p− silicon 421 and associatedbonding/isolation oxide 422.Step (F): FIG. 4F illustrates the structure on after Step (F). Gatedielectric 426 and gate electrode 424 are then deposited following whicha CMP is done to planarize the gate electrode 424 regions. Lithographyand etch are utilized to define gate regions.Step (G): FIG. 4G illustrates the structure after Step (G). Using thehard mask defined in Step (F), p− regions not covered by the gate areimplanted to form n+silicon regions 428. Spacers are utilized duringthis multi -step implantation process and layers of silicon present indifferent layers of the stack have different spacer widths to accountfor lateral straggle of buried layer implants. Bottom layers could havelarger spacer widths than top layers. A thermal annealing step, such asa RTA or spike anneal or laser anneal or flash anneal, is then conductedto activate n+ doped regions.Step (H): FIG. 4H illustrates the structure after Step (H). A siliconoxide layer 430 is then deposited and planarized. The silicon oxidelayer is shown transparent in the figure for clarity, along withword-line (WL) 432 and source-line (SL) 434 regions.Step (I): FIG. 4I illustrates the structure after Step (I). Vias areetched through multiple layers of silicon and silicon dioxide as shownin the figure. A resistance change memory material 436 is then deposited(preferably with atomic layer deposition (ALD)). Examples of such amaterial include hafnium oxide, which is well known to change resistanceby applying voltage. An electrode for the resistance change memoryelement is then deposited (preferably using ALD) and is shown aselectrode/BL contact 440. A CMP process is then conducted to planarizethe surface. It can be observed that multiple resistance change memoryelements in series with transistors are created after this step.Step (J): FIG. 4J illustrates the structure after Step (J). BLs 438 arethen constructed. Contacts are made to BLs, WLs and SLs of the memoryarray at its edges. SL contacts can be made into stair-like structuresusing techniques described in “Bit Cost Scalable Technology with Punchand Plug Process for Ultra High Density Flash Memory,” VLSI Technology,2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka,H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contactscan be constructed to them. Formation of stair-like structures for SLscould be done in steps prior to Step (I) as well.FIG. 4K shows cross-sectional views of the array for clarity.A 3D resistance change memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines—e.g., source-lines SL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut.

While explanations have been given for formation of monolithic 3Dresistive memories with ion-cut in this section, it is clear to oneskilled in the art that alternative implementations are possible. BL andSL nomenclature has been used for two terminals of the 3D resistivememory array, and this nomenclature can be interchanged. Moreover,selective epi technology or laser recrystallization technology could beutilized for implementing structures shown in FIG. 3A-3J and FIG. 4A-4K.Various other types of layer transfer schemes that have been describedin Section 1.3.4 of the parent application can be utilized forconstruction of various 3D resistive memory structures. One could alsouse buried wiring, i.e. where wiring for memory arrays is below thememory layers but above the periphery. Other variations of themonolithic 3D resistive memory concepts are possible.

While resistive memories described previously form a class ofnon-volatile memory, others classes of non-volatile memory exist. NANDflash memory forms one of the most common non-volatile memory types. Itcan be constructed of two main types of devices: floating-gate deviceswhere charge is stored in a floating gate and charge-trap devices wherecharge is stored in a charge-trap layer such as Silicon Nitride.Background information on charge-trap memory can be found in “IntegratedInterconnect Technologies for 3D Nanoelectronic Systems”, Artech House,2009 by Bakir and Meindl (“Bakir”) and “A Highly Scalable 8-Layer 3DVertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried ChannelBE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue,et al. The architectures shown in FIG. 5A-5G are relevant for any typeof charge-trap memory.

FIGS. 5A-5G describes a memory architecture for single-crystal 3Dcharge-trap memories, and a procedure for its construction. It utilizesjunction-less transistors. No mask is utilized on a “per-memory -layer”basis for the monolithic 3D charge-trap memory concept shown in FIG.5A-5G, and all other masks are shared between different layers. Theprocess flow may include several steps as described in the followingsequence.

Step (A): Peripheral circuits 502 are first constructed and above this alayer of silicon dioxide 504 is deposited. FIG. 5A shows a drawingillustration after Step (A).Step (B): FIG. 5B illustrates the structure after Step (B). A wafer ofn+ Silicon 508 has an oxide layer 506 grown or deposited above it.Following this, hydrogen is implanted into the n+ Silicon wafer at acertain depth indicated by 514. Alternatively, some other atomic speciessuch as Helium could be implanted. This hydrogen implanted n+ Siliconwafer 508 forms the top layer 510. The bottom layer 512 may include theperipheral circuits 502 with oxide layer 504. The top layer 510 isflipped and bonded to the bottom layer 512 using oxide-to-oxide bonding.Step (C): FIG. 5C illustrates the structure after Step (C). The stack oftop and bottom wafers after Step (B) is cleaved at the hydrogen plane514 using either a anneal or a sideways mechanical force or other means.A CMP process is then conducted. A layer of silicon oxide 518 is thendeposited atop the n+ Silicon layer 516. At the end of this step, asingle-crystal n+ Si layer 516 exists atop the peripheral circuits, andthis has been achieved using layer-transfer techniques.Step (D): FIG. 5D illustrates the structure after Step (D). Usingmethods similar to Step (B) and (C), multiple n+ silicon layers 520 areformed with silicon oxide layers in between.Step (E): FIG. 5E illustrates the structure after Step (E). Lithographyand etch processes are then utilized to make a structure as shown in thefigure.Step (F): FIG. 5F illustrates the structure after Step (F). Gatedielectric 526 and gate electrode 524 are then deposited following whicha CMP is done to planarize the gate electrode 524 regions. Lithographyand etch are utilized to define gate regions. Gates of the NAND string536 as well gates of select gates of the NAND string 538 are defined.Step (G): FIG. 5G illustrates the structure after Step (G). A siliconoxide layer 530 is then deposited and planarized. It is showntransparent in the figure for clarity. Word-lines, bit-lines andsource-lines are defined as shown in the figure. Contacts are formed tovarious regions/wires at the edges of the array as well. SL contacts canbe made into stair-like structures using techniques described in “BitCost Scalable Technology with Punch and Plug Process for Ultra HighDensity Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol.,no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.;Oomura, M.; et al., following which contacts can be constructed to them.Formation of stair-like structures for SLs could be performed in stepsprior to Step (G) as well.A 3D charge-trap memory has thus been constructed, with (1)horizontally-oriented transistors—i.e. current flowing in substantiallythe horizontal direction in transistor channels, (2) some of the memorycell control lines—e.g., bit lines BL, constructed of heavily dopedsilicon and embedded in the memory cell layer, (3) side gatessimultaneously deposited over multiple memory layers for transistors,and (4) monocrystalline (or single-crystal) silicon layers obtained bylayer transfer techniques such as ion-cut. This use of single-crystalsilicon obtained with ion-cut is a key differentiator from past work on3D charge-trap memories such as “A Highly Scalable 8-Layer 3DVertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried Channel BE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue, etal. that used polysilicon.

While FIGS. 5A-5G give two examples of how single-crystal silicon layerswith ion-cut can be used to produce 3D charge-trap memories, the ion-cuttechnique for 3D charge-trap memory is fairly general. It could beutilized to produce any horizontally-oriented 3D monocrystalline-siliconcharge-trap memory.

While the 3D DRAM and 3D resistive memory implementations in Section 3and Section 4 have been described with single crystal siliconconstructed with ion-cut technology, other options exist. One couldconstruct them with selective epi technology. Procedures for doing thesewill be clear to those skilled in the art.

FIGS. 6A-6B show it is not the only option for the architecture to havethe peripheral transistors, such as periphery 602, below the memorylayers, including, for example, memory layer 604, memory layer 606,and/or memory layer 608. Peripheral transistors, such as periphery 610,could also be constructed above the memory layers, including, forexample, memory layer 604, memory layer 606, and/or memory layer 608,and substrate or memory layer 612, as shown in FIG. 6B. This peripherylayer would utilize technologies described in this application; parentapplication and incorporated references, and could utilize transistors,for example, junction-less transistors or recessed channel transistors.

The monolithic 3D integration concepts described in this patentapplication can lead to novel embodiments of poly-silicon-based memoryarchitectures as well. Poly silicon based architectures couldpotentially be cheaper than single crystal silicon based architectureswhen a large number of memory layers need to be constructed. While thebelow concepts are explained by using resistive memory architectures asan example, it will be clear to one skilled in the art that similarconcepts can be applied to NAND flash memory and DRAM architecturesdescribed previously in this patent application.

FIGS. 7A-7E show one embodiment of the current invention, wherepolysilicon junction-less transistors are used to form a 3Dresistance-based memory. The utilized junction-less transistors can haveeither positive or negative threshold voltages. The process may includethe following steps as described in the following sequence:

Step (A): As illustrated in FIG. 7A, peripheral circuits 702 areconstructed above which a layer of silicon dioxide 704 is made.Step (B): As illustrated in FIG. 7B, multiple layers of n+dopedamorphous silicon or polysilicon 706 are deposited with layers ofsilicon dioxide 708 in between. The amorphous silicon or polysiliconlayers 706 could be deposited using a chemical vapor deposition process,such as LPCVD or PECVD.Step (C): As illustrated in FIG. 7C, a Rapid Thermal Anneal (RTA) isconducted to crystallize the layers of polysilicon or amorphous silicondeposited in Step (B). Temperatures during this RTA could be as high as700° C. or more, and could even be as high as 800° C. The polysiliconregion obtained after Step (C) is indicated as 710. Alternatively, alaser anneal could be conducted, either for all layers 706 at the sametime or layer by layer. The thickness of the oxide 704 would need to beoptimized if that process were conducted.Step (D): As illustrated in FIG. 7D, procedures similar to thosedescribed in FIGS. 3E-3H are utilized to construct the structure shown.The structure in FIG. 7D has multiple levels of junction-less transistorselectors for resistive memory devices. The resistance change memory isindicated as 736 while its electrode and contact to the BL is indicatedas 740. The WL is indicated as 732, while the SL is indicated as 734.Gate dielectric of the junction-less transistor is indicated as 726while the gate electrode of the junction-less transistor is indicated as724, this gate electrode also serves as part of the WL 732. Siliconoxide is indicated as 730.Step (E): As illustrated in FIG. 7E, bit lines (indicated as BL 738) areconstructed. Contacts are then made to peripheral circuits and variousparts of the memory array as described in embodiments describedpreviously.

FIG. 8A-F show another embodiment of the current invention, wherepolysilicon junction-less transistors are used to form a 3Dresistance-based memory. The utilized junction-less transistors can haveeither positive or negative threshold voltages. The process may includethe following steps occurring in sequence:

Step (A): As illustrated in FIG. 8A, a layer of silicon dioxide 804 isdeposited or grown above a silicon substrate without circuits 802.Step (B): As illustrated in FIG. 8B, multiple layers of n+dopedamorphous silicon or polysilicon 806 are deposited with layers ofsilicon dioxide 808 in between. The amorphous silicon or polysiliconlayers 806 could be deposited using a chemical vapor deposition process,such as LPCVD or PECVD abbreviated as above.Step (C): As illustrated in FIG. 8C, a Rapid Thermal Anneal (RTA) orstandard anneal is conducted to crystallize the layers of polysilicon oramorphous silicon deposited in Step (B). Temperatures during this RTAcould be as high as 700° C. or more, and could even be as high as 1400°C. The polysilicon region obtained after Step (C) is indicated as 810.Since there are no circuits under these layers of polysilicon, very hightemperatures (such as 1400° C.) can be used for the anneal process,leading to very good quality polysilicon with few grain boundaries andvery high mobilities approaching those of single crystal silicon.Alternatively, a laser anneal could be conducted, either for all layers806 at the same time or layer by layer at different times.Step (D): This is illustrated in FIG. 8D. Procedures similar to thosedescribed in FIG. 32E-H are utilized to get the structure shown in FIG.8D that has multiple levels of junctionless transistor selectors forresistive memory devices. The resistance change memory is indicated as836 while its electrode and contact to the BL is indicated as 840. TheWL is indicated as 832, while the SL is indicated as 834. Gatedielectric of the junction -less transistor is indicated as 826 whilethe gate electrode of the junction-less transistor is indicated as 824,this gate electrode also serves as part of the WL 832. Silicon oxide isindicated as 830Step (E): This is illustrated in FIG. 8E. Bit lines (indicated as BL838) are constructed. Contacts are then made to peripheral circuits andvarious parts of the memory array as described in embodiments describedpreviously.Step (F): Using procedures described in Section 1 and Section 2 of thispatent application's parent, peripheral circuits 898 (with transistorsand wires) could be formed well aligned to the multiple memory layersshown inStep (E). For the periphery, one could use the process flow shown inSection 2 where replacement gate processing is used, or one could usesub-400° C. processed transistors such as junction-less transistors orrecessed channel transistors. Alternatively, one could use laser annealsfor peripheral transistors' source-drain processing. Various otherprocedures described in Section 1 and Section 2 could also be used.Connections can then be formed between the multiple memory layers andperipheral circuits. By proper choice of materials for memory layertransistors and memory layer wires (e.g., by using tungsten and othermaterials that withstand high temperature processing for wiring), evenstandard transistors processed at high temperatures (>1000° C.) for theperiphery could be used.

It will also be appreciated by persons of ordinary skill in the art thatthe invention is not limited to what has been particularly shown anddescribed hereinabove. For example, drawings or illustrations may notshow n or p wells for clarity in illustration. Further, combinations andsub-combinations of the various features described hereinabove may beutilized to form a 3D IC based system. Rather, the scope of theinvention includes both combinations and sub-combinations of the variousfeatures described hereinabove as well as modifications and variationswhich would occur to such skilled persons upon reading the foregoingdescription. Thus the invention is to be limited only by the appendedclaims.

What is claimed is:
 1. A 3D semiconductor device, the device comprising:a first level comprising a first single crystal layer; first transistorsoverlaying said first single crystal layer; second transistorsoverlaying said first transistors; and a second level comprising asecond single crystal layer, said second level overlays said secondtransistors, wherein said first transistors and said second transistorseach comprises a polysilicon channel.
 2. The device according to claim1, wherein said first transistors and said second transistors arejunction-less transistors, wherein each of said junction-lesstransistors comprises a source, a channel, and a drain, and wherein saidsource, said channel, and said drain comprise a similar doping type. 3.The device according to claim 1, wherein said first level comprises avia through said first single crystal layer.
 4. The device according toclaim 1, wherein said second level comprises a via through said secondsingle crystal layer.
 5. The device according to claim 1, wherein saidfirst transistors and said second transistors are self-aligned, beingprocessed following the same lithography step.
 6. The device accordingto claim 1, wherein said device comprises an array of memory cells,wherein a plurality of said memory cells comprises at least one of saidsecond transistors, and wherein said second level comprises a peripherycircuit to control said array of memory cells.
 7. The device accordingto claim 1, wherein said second single crystal layer comprises thirdtransistors, and wherein said third transistors are aligned to saidfirst transistors with less than 150 nm misalignment.
 8. A 3Dsemiconductor device, the device comprising: a first level comprising afirst single crystal layer; first transistors overlaying said firstsingle crystal layer; second transistors overlaying said firsttransistors; and a second level comprising a second single crystallayer, said second level overlaying said second transistors, whereinsaid first transistors and said second transistors are junction-lesstransistors.
 9. The device according to claim 8, wherein saidjunction-less transistors each comprise a source, a channel, and adrain, and wherein said source, said channel, and said drain have asimilar doping type.
 10. The device according to claim 8, wherein saidsecond transistors each comprise a polysilicon channel.
 11. The deviceaccording to claim 8, wherein said first level comprises a via throughsaid first single crystal layer.
 12. The device according to claim 8,wherein said second level comprises a via through said second singlecrystal layer.
 13. The device according to claim 8, wherein said firsttransistors and said second transistors are self-aligned, beingprocessed following the same lithography step.
 14. The device accordingto claim 8, wherein said device comprises an array of memory cells,wherein a plurality of said memory cells comprise at least one of saidsecond transistors, and wherein said second level comprises a peripherycircuit to control said array of memory cells.
 15. A 3D semiconductordevice, the device comprising: a first level comprising a first singlecrystal layer; first transistors overlaying said first single crystallayer; second transistors overlaying said first transistors; thirdtransistors overlaying said second transistors; fourth transistorsoverlaying said third transistors; a second level comprising a secondsingle crystal layer, said second single crystal layer overlaying saidfourth transistor, wherein said second transistors, said thirdtransistors, and said fourth transistors are self-aligned, beingprocessed following the same lithography step; and a memory peripheralcircuit, wherein said memory peripheral circuit comprises at least oneof said first transistors, and wherein said memory peripheral circuitcontrols at least one of said second transistors, at least one of saidthird transistors, and at least one of said fourth transistors.
 16. Thedevice according to claim 15, wherein at least one of said thirdtransistors comprises a source, channel, and drain, and wherein saidsource, said channel, and said drain have a similar doping type.
 17. Thedevice according to claim 15, wherein said third transistors eachcomprise a polysilicon channel.
 18. The device according to claim 15,wherein said first level comprises connections to an external device,and wherein said connection comprises a via through said first singlecrystal layer.
 19. The device according to claim 15, wherein said secondlevel comprises fifth transistors, wherein said fifth transistors eachcomprise a transistor channel, and wherein said transistor channelcomprises said second single crystal.
 20. The device according to claim15, further comprising: a memory cell, wherein said memory cellcomprises at least one of said third transistors.